1. Field of the Invention
The present invention particularly relates to an image forming apparatus, an image forming method and a program that variably magnify and form an image of an electronic document file including a drawing of a tile image.
2. Description of the Related Art
In many recent printer products, a touch panel including UI as an operation panel is mounted. A media-direct print capability in which a user can connect a storage device, such as an SD card or a USB storage, to a printer, and directly perform selection of an electronic document file stored in the storage device, print setting, and print instruction via an operation panel is widely spreading. With the spread of this type of printer, the method of using electronic document files is being diversified.
In the case of printing from a printer driver having been used so far, appropriate print data according to an output resolution is prepared from an electronic document file at each printing. Thus, even if the print data is output as it is, no deterioration in an image quality, such that a tile pattern included in the electronic document file is lost, occurs and a desirable print result can be obtained.
On the other hand, with the diversification of the method of using electronic document files, print data is sometimes output in various modes. When the electronic document file is to be printed, an output resolution different from the resolution specified when the print data was created can be specified at image formation. For example, as a printing setting, an output resolution can be specified for printing a poster in which one logical page in PDL data can be imposed on a plurality of physical pages of output sheets. Alternatively, the output resolution can be specified for imposition printing in which a plurality of logical pages in the PDL data is imposed on one physical page of an output sheet. Also, in the media-direct printing, a function called index printing might be incorporated. This is a function of reducing and printing a specified arbitrary file as a list. If the resolution of the data is different from the resolution to be output as above, so-called variable magnification processing is required.
Thus, a scalable expression using a path and the like not depending on the resolution is used in the drawing description in an electronic document file, in general, and a desirable output result is obtained even in the case of output with a different resolution by the variable magnification processing. However, many of bitmap data and mask data in the electronic document file are stored in a data format depending on the resolution. If the data dependent on the resolution is output by specifying a variable magnification, there has been a problem that a pixel is missing or only specific lines are overlapped and the like.
In order to prevent such a problem, a method of forming an image with a desired resolution by variably magnifying the tile image itself has been known as a prior-art technology. For example, a technology is known in which a denominator to a density of a tile image and a denominator of a variable magnification rate are both set at prime numbers to each other so as to suppress the occurrence of an interference pattern (See Japanese Patent Laid-Open No. H06-214554 (1994), for example).
However, even if such prior-art technologies are used, the density of the tile image drawn after variable magnification might be different from that of the original tile image before the variable magnification. Also, a characteristic (a checkered pattern, a vertical line, a diagonal line and the like, for example) of the original tile might be lost by the magnifying/reducing method of the tile image.
On the other hand, a technology of variable magnification to a desired resolution after image formation with a resolution of the PDL data is also known. For example, if a copy-forgery-inhibited pattern and print data are to be combined, a technology is known in which the copy-forgery-inhibited pattern is divided into some regions and variably magnified, while a tile pattern in them is maintained (See Japanese Patent laid-Open No. 2005-198250, for example).
If an appropriate image variable magnification algorithm is used for an image to be variably magnified as above, a desirable output image can be obtained. However, since the image size for one page is extremely large, it is disadvantageous in terms of a used amount of memory. In the case of an A4-sized RGB image, it has approximately 100 MB in terms of a RAW image. If an appropriate variable magnification algorithm considering surrounding pixels is used, the calculation amount is also increased, which may also be disadvantageous in terms of performance.